Speech compression involves the compression of audio data in the form of speech. Speech is a somewhat unique form of audio data, with a number of needs which must be addressed during compression to ensure that it will be intelligible and reasonably pleasant to listen to. A number of software programs have been designed specifically with speech compression in mind, including programs which can perform additional functions such as encrypting the compressed data for security.
Raw audio data can take up a great deal of memory. During compression, the data is compressed so that it will occupy less space. This frees up room in storage, and it also becomes important when data is being transmitted over a network. On a mobile phone network, for example, if speech compression is used, more users can be accommodated at a given time because less bandwidth is needed. Likewise, speech compression becomes important with teleconferencing and other applications; sending data is expensive, and anything which reduces the volume of data which needs to be sent can help to cut costs.
Speech is a relatively simple and widely studied type of audio data, which makes it easy to compress in some ways. However, it is important to ensure that compression retains the integrity of the speech. If the data becomes distorted in some way, it can be difficult to understand, and it can also be hard to listen to. Thus, speech compression needs to be performed in a way which retains the key qualities of the data. It is easy for speech to song “wrong” to a listener, interfering with understanding of the transmitted data.
Programs which handle the creation of audio files may have a compression option available. After recording or generating the raw audio file, people can choose between a number of parameters to get the file compressed to a more manageable size. Speech compression can also be done on the fly, as when people use cell phones and the network compresses the data while generating a data signal so that people can talk in real time.
If the data also needs to be encrypted, this may be done in real time or in a second pass which encrypts the compressed data. In this case, someone who wants to hear the speech will need to decrypt the data and run it through a program, which may be embedded into a piece of equipment such as a secured phone, which is capable of reading compressed data.